Phase Equilibria in the Ni–Rich Region of the Ni–Al–Zr System

Abstract

Alloys from the Ni–rich corner of the Ni–Al–Zr system have potential for use in high temperature, high strength applications. Such applications require a detailed knowledge of the high temperature phase equilibria.In the case of the Ni–Al–Zr system no isothermal sections have been published although the existence of a monovariant eutectic valley between Ni3Al and Ni7Zr2 has been established. An experimental determination of the phase equilibria in this system is being carried out using quantitative electron microprobe analysis (JEOL JSM–U3), xray diffraction and optical metallography. Partial isothermal sections are being determined for 1373K (1100°C) and 1273K (1000°C) and the resulting phase equilibria compared to that in the Ni–Al–Hf system determined previously.

Isothermal Sections of Al-Ni-Zr Ternary System at 850 and 1050 °C

“…This phase region (b + Ni 7 Zr 2 ) observed here is consistent with the phase relationships determined by Jay. [30,31] In sample #5 (Al-80Ni-10Zr) quenched from 1050°C, a three phase microstructure was observed (Fig. 5(c)).…”

“…c¢ + Ni 5 Zr + Ni 7 Zr 2 , differs from that obtained in Bur [29] and Jay. [30,31] As pointed out by Nash, [32] the number of samples measured by Bur [29] is not enough to obtain exact phase relation. So, we thought that the phase equilibrium should be Ni 5 Zr + Ni 7 Zr 2 + c¢.…”

“…By SEM-EDS analysis it is known that there is a three-phase region consisted of bright Ni 7 Zr 2 , gray s 2 and dark AlNi(b), further confirmed through XRD analysis. This three-phase region also existed in the isothermal sections of Jay, [30,31] but did not appear in that of Bur. [29] In light of the review of Nash, [32] the presently measured equilibrium Ni 7 Zr 2 + s 2 + AlNi(b) should be accepted.…”

“…Note here, the determined phase region of Ni 5 Zr + c is wider than that reported previously. [30,31] The BES micrograph of sample #2 (Al-61.6Ni-7Zr) is showed in Fig. 5(b), where two different phases (dark and bright phases) are distinguished.…”

“…The phase equilibrium (c + c¢ + Ni 5 Zr) observed here is different from the phase relation (c + c¢ + Ni 7 Zr 2 ) reported by Jay. [30,31] Ghosh [33] pointed out that the equilibria obtained by Jay [30,31] were not exact due to inconsistency between their x-ray data and electron microprobe analysis. In addition, this phase equilibrium (c + c¢ + Ni 5 Zr) has also been observed in our work at 850°C.…”